Flexible means for measuring liquid level

ABSTRACT

The invention contemplates a unitary magnetically sensitive circuit element or network and a flexibly articulatable elongate assembly of a plurality of such elements or networks, with electrical interconnection of the same, such assembly being inherently suited to precision operation as a function of length, whatever the length selected for a particular application or use. In one application to liquid-depth indication within a tank, the longate assembly is merely inserted into the tube along which a float-borne permanent magnet is guided, and the magnetically sensitive element of each successive unit is actuated as the float tracks liquid level and is displaced from actuating relation with one and then to the nextadjacent one of the circuit-element units. The connection of circuit-element units is such that electrical-resistance observation from one end of the assembly provides a direct indication of the liquid level at which the float magnet is currently operative. Various forms and a method of manufacture are described.

This application is a continuation of application Ser. No. 417,455 filedSept. 13, 1982, now abandoned, which is a continuation of applicationSer. No. 093,181 filed Nov. 13, 1979, which was a division ofapplication Ser. No. 912,218 filed June 5, 1978.

The invention relates to an improved elemental and assembledmagnetically-sensitive unitary structure, specifically embodying asealed magnetic-reed switch element, as for use in a depth-sensingtransmitter for tank-level indicating purposes.

Present practice in the construction of depth-sensing transmitters ofthe character indicated in painstakingly and precisely to mount pluralmagnetic-reed switch elements and their associated network resistorelements to a rigid elongate base, all performed as individualoperations at the factory, and all preassembled to ultimate specifiedlength and network constants, within a protective guide tube, prior toshipment from the factory. The technique is laborious, and each job isfabricated on what amounts to essentially a custom basis.

It is an object of the invention to provide an improved construction ofthe character indicated.

It is also an object to provide for use in such construction a unitarynetwork assembly or module which includes a switch element of thecharacter indicated and which lends itself to selective use in suchinterconnected multiples as may be required for various specificapplications.

It is another object to provide an electrically interconnected elongateassembly of switch-element networks, of such nature as to be directlyutilizable in interconnected multiple after cut-off from the elongatelength.

Another object is to achieve the above objects with an elemental networkconstruction in which all structural parts are embedded in pottingmaterial, with externally projecting terminals positioned for correctelectrical interconnection of plural such networks in cascaded multiple,as cooperating parts of the same transmitter.

A further object is to provide a multiple-unit assembly of the characterindicated wherein the interconnected networks are capable of flexiblearticulation with respect to each other; specifically, such flexibilityis desired as to enable coiled lay-up of the elongate assembly, forshipping purposes, and to enable cut-off to length as may be needed fora variety of on-site installation purposes.

It is another object to provide an elemental construction of thecharacter indicated and lending itself to mass-production of networkunits, as well as to mass-production of an elongate flexible assembly ofsuch units.

It is a general object to meet the above objects with the high degree ofaccuracy inherent in present custom constructions and which,additionally, permits far greater latitude in primary assembly phases,improves shipping characteristics, and greatly simplifies on-siteinstallation.

Other objects and various further features of novelty and invention willbe pointed out or will occur to those skilled in the art from a readingof the following specification in conjunction with the accompanyingdrawings.

In said ddrawings, which show, for illustrative purposes only, preferredforms and methods of the invention:

FIG. 1 is a simplified view in perspective of an encapsulated elementalswitch-element network unit of the invention, in exploded relation to aflexible carrier or base strip to which it is to be assembled;

FIG. 2 is a simplified fragmentary vertical sectional view of a tank andliquid-level mechanism in which the network of FIG. 1 may be embodied;

FIG. 3 is a simplified view in perspective of the network of FIG. 1 withupper encapsulation removed, to display an illustrative internalarrangement of component elements;

FIG. 4 is a fragmentary longitudinal sectional view to show an assembledarray of a plurality of the network units of FIG. 1;

FIG. 5 is a simplified electrical diagram to show cooperative electricalfunctioning of units interconnected as in FIG. 4;

FIG. 6 is a view in perspective to illustrate a supply reel or spoolsuitable for coiled shipment and pay-out of an elongate assembly of thenature shown in FIG. 4;

FIGS. 7 to 10 are similar plan views to illustrate stages of amanufacturing technique for making the individual network units of FIG.1;

FIG. 11 is a plan view of an individual network unit produced by thetechnique of FIGS. 7 to 10;

FIG. 11A is a plan view of offal remaining after making plural units ofFIG. 11;

FIG. 12 is a multiple-fragment plan view of a flexibly connected arrayof network units representing a modified construction and method, theseparate fragments being identified a, b and c to illustrate successivemanufacturing steps;

FIG. 13 is a view in side elevation, applicable to fragment c of FIG.12;

FIG. 14 is a fragmentary andd partly broken-away perspective view toillustrate another modification;

FIGS. 15 and 16 are an illustration of a pulse-counting application ofthe invention;

FIG. 17 is a circuit diagram of a series array of encapsulated units;and

FIG. 18 is another liquid volume application of the invention.

The invention will first be described in application as atank-level-indicating (TLI) insert, comprising a plurality ofencapsulated network units 10 assembled to a flexible elongate basestrip or carrier 11, which may be of insulating material such as afiber-glass-filled plastic. Each encapsulated unit 10 is elongate andgenerally rectangularly prismatic and is equipped with stiffly compliantflat projecting terminal-strip elements 12-13 at one end and 14-15 atthe opposite end, elements 12-13-14-15 being all downwardly bent asmounting lugs or legs which extend sufficiently below the body of unit10 to pass through and to project beyond corresponding anchoringapertures 12'-13'-14'-15' in the carrier 11. Notched shoulderformations, as at 16, limit terminal-lug insertion into the indicatedapertures, at a point establishing a unit-body clearance d (FIG. 4) ofbody 10 above carrier 11, and the lugs 14-15 of the next-adjacent unitto the left of unit 10 in FIG. 1 will be understood to use the sameapertures 12'-13' as are shown in FIG. 1 to accept insertion of lugs12-13 of unit 10 of FIG. 1.

To complete multiple-unit assembly to the carrier 11, the terminal lugs12-14 and 13-15 of adjacent ends of adjacent units are first twistedtogether below the lower surface of the carrier and are then solderedfor permanent electrical connection, the profile of the soldering beadbeing illustratively shown by phantom outlines 17 in FIG. 4; preferably,the described fit of two lugs (e.g., 13-15) into a single aperture(e.g., 13') is snug, to enable positive development of the describedtwist and to enable each solder bead 17 to provide a positive stopagainst later removal from assembled relation to carrier 11. Preferablyalso, the described multiple-unit assembly to carrier 11 is thereafterassembled as by insertion into a pliant encasing envelope 18 of tubing,such as vinyl or polyethylene tubing, for protection of the solderedconnections and for greater ease of handling and manipulation.

In the illustrative tank-level application of FIG. 2, the describedelongate TLI transmitter insert of FIG. 4 will be understood to beinserted into and vertically oriented within a non-magnetic rigidsupporting tube 20, supported from a suitable fitting 21 through theremovable cover plate 22 for service access via a flanged port 23 in aliquid vessel or tank 24. An annular float 25 is shown guided by tube 20and will be understood to carry permanent-magnet means (not specificallyshown) of such strength as to operate the one or more magneticallysensitive elements of adjacent units 10 in instantaneous magnetic-fieldproximity thereto. The tube 20 may be straight and vertical, but Isuggest at the lower portion 20' thereof that it may also be curved, asto adapt to the contour of a side tank in a ship, the TLI insert of FIG.4 being understood to flexibly adapt to such contour in the course ofinsertion into tube 20. A junction box 26 and a remote conduitconnection thereto are shown for accommodation of electrical connectionsbetween the TLI transducer and associated remote electricalinstrumentation.

In the form shown, the encapsulation of the electrical networkassociated with each unit 10 comprises upper and lower nested casinghalves 28-29 which will be understood to contain circuit elements of thenetwork, as well as anchored portions of all terminal-strip elements12-13-14-15, the anchoring being established by a solid plastic pottingembedment of said elements within and to the inner wall surfaces of thecasing halves. However, for sake of clarity in FIG. 3, the potting hasbeen omitted to reveal the network elements as a glass-encasedmagnetic-reed switch 30, a first or voltage-dividing resistor 31 and asecond or averaging resistor 32. Also revealed in FIG. 3 is a solid busconnection strip 33 from the longitudinal ends of which both of theterminal lugs 12-14 integrally extend; in contast, the anchored ends ofterminal lugs 13-15 project toward each other but are connected only bythe leads of resistor 31. The switch element 30 forms part of meansconnecting one end of resistor 31 to the bus connection 33, and in theform shown this is a series connection with the averaging resistor 32,the series connection being established via a lug strip 34 which ispartly anchored (by potting embedment within casing 28-29) and which ispartly externally exposed at one longitudinal end of the unit, forunambiguous interpretation of the parts relationship within the pottedcasing.

The described arrangement of network parts within the potted unit isdepicted in electrical-circuit symbolism in FIG. 5, which also depictsthe relationship of coacting plural networks, resulting from thedescribed assembly of units 10 (FIG. 4). Thus interconnected, the buselements 33 are seen to define a single conductive line which can beterminated at its upper end at a first terminal-lead connection A to theterminal lug 12 of the uppermost end of the uppermost unit 10; thedesignation A will be understood to suggest preferably an insulatedflexible conductor which may be threaded through a first lead apertureA' at the upper end of carrier 11, for flexible-lead accessibility atjunction box 26. Thus interconnected, each resistor 31 is seen as one ofa plurality of series-connected elements of a voltage divider, availablefor tapping to line 33, depending upon the level at which switch 30 (orswitches 30) of an adjacent one or more units 10 is currently operated(closed) by the float magnet; the upper end of this voltage divider isaccessible via a second terminal lead connection B to the terminal lug13 of the uppermost end of the uppermost unit 10, and the designation Bwill be understood to suggest preferably a second insulated flexibleconductor which may be threaded through a second lead aperture B' at theupper end of carrier 11.

To complete electrical connections of the TLI transmitter, a thirdinsulated flexible conductor 35 will be understood to be connected tothe lowermost terminal lug 15 of the lowermost unit 10 and to extend toan upper terminal lead C, via a third threading aperture C' at the upperend of carrier 11. The legend in FIG. 5 suggests that excitation voltageis applied across the voltage divider at leads B-C, and of coursedepth-indicating readings may be measured across lead A and one or theother of leads B-C, depending upon the desired direction of readingdepth of liquid (or liquid clearance from the top of the tank).

FIG. 6 illustrates that an elongate array of switchnetwork units 10 on acarrier 11, and protectively shrouded by flexible tubing 18, lendsitself to coiled storage, shipment or other handling, for example on andbetween side flanges of a spool 37 of the type customarily used forhandling electrical cable. Preferably, the tubing 18 is transparent sothat all units 10 therein are visible, thus aiding clean cut-off of adesired smaller plurality as needed for a given on-site TLI-insertinstallation or TLI-insert replacement.

FIGS. 7 to 11 illustrate successive steps in a method of manufacturingindividual network units 10 on a mass-production basis, which may befully automated, if desired. The method commences with formation of asuitable multiple-element lead-frame blank 40 (FIG. 7) which is shownwith eight repeats (a-b-c-d-e-f-g-h) of the identical cut-out orlattice-like pattern of integrally interconnected conductive strips. Theblank 40 may be formed by known photographic etching and/or depositiontechniques; however, I prefer that it be punched out from a singlediscrete rectangular sheet of conductive metal (e.g., brass or copper)of the overall dimensions M-N shown, or that it be progressively stampedfrom a continuously paid-out length of strip material of width N, aswill be understood.

The patterns a . . . h are all defined between and integrally formedwith elongate side-frame members 41-42 which, in the longitudinal senseof each of the individual patterns a . . . h, may be considered aslongitudinal-end-frame members. Frame member 41 has locating circularapertures 43 in register with each of the patterns a . . . h, and framemember 42 has similar but oblong apertures 44, for accurate andunambiguous tool-positioning register with these particular framemembers. Patterns a . . . h are also defined between and integrallyformed with connecting frame members which integrally connect members41-42 and which are identified 45-46, for the case of the two adjacentconnecting frame members which define the opening for pattern c, takenas illustrative. Thus, the illustrative pattern c will be understood tobe integral with and contained within its own frame, comprisinglongitudinally extending elongate side-frame members 45-46 and end-framemembers 41-42.

Each lattice-like pattern of the blank 40 comprises interconnectedstrips which are connected (a) by a first severable-strip portion 47connecting the elongate side-frame members 45-46 near but spaced fromthe end 41 of the frame and (b) by a second severable-strip portion 48connecting the elongate side-frame members 45-46 near but spaced fromthe other end 42 of the frame. Two laterally spaced terminal-stripportions 49-50 are integral with and in longitudinal cantileveredprojection from the severable strip 47, in the direction of and short ofthe adjacent end frame 41; similarly, two laterally spacedterminal-strip portions 51-52 project from the severable strip 48, inthe opposite direction and short of the adjacent end frame 42. Abus-strip portion 53 is near but laterally spaced from the adjacentelongate side frame 45 and integrally connects the severable-stripportions 47-48 at generally the alignment of the terminal-strip portions49-51 which are near said elongate side frame 45. A first mounting-stripportion 54 is integral with and in cantilevered projection from thefirst severable-strip portion 57 and extends in the direction of theremote frame end 42 and at generally the alignment of the associatedterminal-strip portion 50, which is near the other elongate side 46 ofthe frame; and similarly, a second mounting-strip portion 55 is integralwith and in cantilevered projection (in the opposite direction) from thesecond severable-strip portion 48, the mounting-strip portion 55 beingshown with a laterally offset dog-leg end, to facilitate circuit-elementassembly, as will become clear. Finally, a third severable-strip portion56 is integral with and in cantilevered projection from the firstseverable-strip portion 47 at an intermediate location, betweenterminal-strip alignments 49-51 and 50-52, the mounting-strip portion 56being shown with a log-leg end and extending in the direction of theremote end 42.

Having formed the blank 40, all is in readiness to accept assembly ofelectrical components 30-31-32 thereto (FIG. 8). Preferably, the leadsto each of these components are trimmed to length as appropriate foroverlapping registry with and soldered connection to the mounting-stripportions 54-55-56, when all components 30-31-32 are in side-by-sidelongitudinally extending adjacency, as shown. Thus, the leads of thedivider resistor 31 are electrically connected to mounting-stripportions 54-55, the leads of switch 30 are electrically connected tomounting-strip portions 55-56, and the leads of resistor 32 areelectrically connected to mounting-strip portion 56 and to a shortoffset 57, forming part of the bus-strip connection 53. It will beunderstood that the described components may be positioned in registerwith their correct mounting-strip portions, and soldered as described,by manual means or by automated means.

Having assembled electrical components to the blank 40, theencapsulation may be performed by transfer molding, unit by successiveunit, or in batches appropriate to the number of units per lead-frameblank 40, here shown as eight. However, in the form illustrated, eachcapsule employs two injection-molded casing halves 28-29 which areinstalled on the lead-frame blank 40, prior to filling the capsules withpotting material such as an epoxy. Thus, the separate casing halves28-29 are fitted to each other via opposite sides of each unit assemblyof components (FIG. 9), it being understood that local edge cut-outs inone or both casing halves permit correct casing location and arelatively tight interfit between casing halves. With the casing halvesthus held to each other and to blank 40 by suitable means (not shown),epoxy potting material is injected via sprue means (suggested by anarrow 58, FIG. 1) extending vertically upward through a central carrieropening and through a registering opening (not shown) in the lowercasing half 29. In spite of the tight and accurate fit of casing halvesto each other and to blank 40, small air-bleed crevices remain to permitair-displacement during the operation of filing with potting material,resulting in some exuded flashing external to the interfit.

After curing, FIG. 10 indicates by legend my preference to place theblank 40 with its load of cured encapsulations into a suitable press forremoval of flashing around all capsules. Thereafter, the loaded blank isplaced in a blanking press to perform all shearing operations needed tosever each encapsulated unit (FIG. 11) from its surrounding frame,leaving an offal comprising essentially the framework 41-42-45-46 (FIG.11A). In this final shearing step, all operations occur only on theseverable strips 47-48, care being taken that the removed scraps aresufficiently short, to define insertion-limiting shoulders at the baseend of all terminal-strip members, as described at 16 in the case ofterminal 12 (defined by terminal-strip portion 49).

The various fragmentary views of FIGS. 12 and 13 illustrate a modifiedconstruction and method of the invention wherein the encapsulated unitsare severably assembled to a continuously elongate lead-frame blank 60.(FIG. 12a), which is the basis of permanent but flexibly articulatedmechanical and electrical end-to-end connection of all units.Significant lead-frame elements described in connection with FIG. 7 willbe recognized as having their counterparts in successive repeats of thelattice-like patterns of blank 60, and therefore these elements in FIG.12a are given the same reference numbers, with primed notation, for thecase of two adjacent unit patterns m, n. Aside from the end-to-endconfiguration of adjacent patterns, the FIG. 12a arrangement differsfrom the blank 40 of FIG. 7 in that there are no end-frame members andno terminal-strip portions; instead, a single severable-strip portion 61integrally connects spaced elongate continuous side-frame members 62-63and integrally also serves both (a) the right-end bus and mountingformations (53'-57'-55') of one unit pattern (m) and (b) the left-endbus and mounting formations (53'-56'-54') of the next-adjacent unitpattern (n). Circuit components 30-31-32 for each successive network areassembled and secured to each unit pattern in the manner alreadydescribed, resulting in the assembled appearance of FIG. 12b; and pottedencapsulation proceeds as already described, resulting in the appearanceof FIG. 12c, after curing, and after trimming the flashing.

In the embodiment and method of FIG. 12, the final blanking step isoperative only on the severable strip 61, namely to cut off connectionsto side-frame members 62-63, and to cut off strip 61 connections on bothlateral sides of mounting-strip portion 56'. Such portions of eachseverable strip 61 as remain after final blanking will be understood toprovide total electrical and mechanically flexible interconnection ofall encapsulated units 10', as shown in FIG. 12c and FIG. 13. Althoughnot shown, it is preferred to complete the continuously elongate arrayby shrouding the same in plastic tubing, as at 18 for the form of FIG.4. The completed article can then be coiled, shipped, and handled asdescribed for FIG. 6, with on-site cut-off (at 61) to length as desired.

FIG. 14 illustrates application of the invention to a flexible insulatedmulti-conductor cable 65 wherein the several conductors 66-67-68 areheld by an insulating body 69 in laterally spaced relation, providing aflat overall section. In this modification, the outer conductors 66-68are allowed to remain continuous, and the center conductor 67 is severedat each desired location of a switch-network unit of the invention. Insevering the conductor 67, body material is also locally removed, to anextent producing a cavity 70 to permit insertion of the switch-networkcomponents into cavity 70 (between conductors 66-68) and theirconnection (a) to the adjacent severed ends of conductor 67 and (b) toan adjacent part of the outer conductor 66. The components 30-31-32 maybe preassembled (i.e., electrically and mechanically connected) to eachother prior to their assembly to cable 65, and their connections toconductors 66-67 are shown by way of crimp connectors 71-72 (for therespective ends of the dividing resistor 31) to severed ends ofconductor 67, and 73 (for the connection of averaging resistor 32) toconductor 66. Upon such assembly, the cavity 70 may be filled and thethus-spliced cable and switch-network may be encapsulated in pottingmaterial as by transfer molding and as suggested with some exaggerationby phantom outline of a capsule-body profile 74. The resulting structureis a flexibly compliant ribbon of cable wherein the outer conductors66-68 maintain longitudinal integrity and sustain all tension forces. Interms of multiple-unit connections, and with reference to FIG. 5, theconductors 66-67-68 will be seen to provide the functions of lines A, B,and C, respectively. Thus, no additional line is needed, the return line(35) connection being established once the cable, with its multipleswitch-network units spliced thereto, has been cutoff to desired length,and once the distant end of conductor 68 (line 35) has been connected tothe adjacent end of conductor 67, as by crimped or soldered connectormeans.

The described embodiments and method of the invention will be seen tohave met all stated objects, providing all the accuracy and reliabilityof custom-made TLI inserts and, at the same time, vastly simplifyingtheir assembly, shipping characteristics and on-site installation. Thedescribed encapsulation eliminates the need for expensiveprinted-circuit boards, and in the case of FIGS. 1 to 4, the onlyrequired connections are two per unit, as described for the twisted andsoldered connection 13-15 in FIG. 4, with addition of one externalreturn wire (35) to complete necessary circuitry. Moreover, theembodiment of FIGS. 13 and 14 is a demonstration that no assemblyconnections are needed beyond the attachment of an external return wire(35) to complete the circuit to the end of the voltage divider at thepoint of cut-off.

The invention will be seen to permit use of miniature, mass-produced,magnetic-reed switches which are currently available, at considerablecost savings over presently used larger switches. These smaller switchesare less than an inch long, from tip to tip of their leads, and theirsmaller length permits capsule design of such length that in theend-to-end array of FIG. 4, a switch-actuating (i.e., depth indicating)resolution of one inch is inherent for the case of a float magnet onlyactuating the closure of one to two switches in alternation, but if themagnet is operative to close two or three switches in alternation, theinherent resolution becomes one-half inch, through selection of suitableresistor values at 31-32. Typically, for a TLI insert of FIG. 4 in useto measure straight vertical depth over a range of 10 feet, this meansan array of 120 switch-network units, and if the float magnet isdesigned to alternate between operation of two and three adjacent switchunits at one time, the unit-divider resistance 31 is 10 ohms, theaveraging resistor 32 is 330 ohms, and thus the total voltage-dividableresistance excited at connections B-C is 1200 ohms.

While the invention has been described in detail for the preferred formsshown, it will be understood that modifications may be made withoutdeparting from the invention. Thus, for example, the return line 35 maybe incorporated into the design of the lead-frame blank (40, 60)analogous to the manner described for FIG. 13, thereby avoiding need foror use of a separate insulated wire 35. Also, the invention will beunderstood to be of greater application than merely as a TLI insert; forexample, successive closure of switches at successive units of the arrayis a method of pulse generation, should pulse-count up and pulse-countdown be the technique employed to identify linear position of theactuating magnet (which need not necessarily be float-borne), e.g., as ameans of measuring distance of displacement of two relatively movablemembers.

FIGS. 15 and 16 are more specifically illustrative of a pulse-countingapplication of the invention, wherein each encapsulated switch unit 75contains but a single electrical component, namely, a magnetic-reedswitch 76 of the character already described. Also, each unit may bemade according to either of the methods already described, namely upon acontinuously elongate lead-frame blank from which continuous connectionsremain after encapsulation and blanking (as in FIGS. 12 and 13), or, asshown, upon a continuously elongate lead-frame blank 77 from whichdiscrete encapsulated units 75 remain after blanking to sever from theframe members 78-79 of the blank 77, resulting in the appearance andcarrier-mountability discussed in connection with FIG. 1. Specifically,the lattice-like lead-frame pattern for each unit 75 is shown tocomprise two like bus connectors 33' integrally and continuouslyconnecting the separate terminal-strip portions 49'-51' and 50'-52'after blanking to sever the severable-strip portions 47'-48', theseverance being at locations indicated generally by heavy dashed lines.The single switch element 76 of each unit is shown with its leadsconnected to lug formations of the bus connectors 33', at the respectiveends of the capsule. Encapsulation, potting and blanking are aspreviously described.

When interconnected by mounting upon a carrier 11, all switches 76 areelectrically in parallel and are precisely spaced from each other.Typically, for pulse-counting as a function of magnet traverse along thelength of the array, a direct-current supply connection is made to thetwo end terminals of the array, via series-connected resistor andtransformer-primary elements 80-81. Each switch closure is thusoperative to produce a polarized pulse in the transformer secondary, apulse of opposite polarity being generated upon each switch opening.Assuming only the first-polarity pulses to be of interest for count-uppurposes, and only the second-polarity pulses to be of interest forcount-down purposes, the remainder of the circuit of FIG. 16 includeslike but oppositely polarized half-wave rectifiers 82-83' to select onlythe desired polarity pulses, pulse-counter means 83-83' for counting thepulses according to the direction of change (i.e., travel), and displayor the like utilization means 84 responding differentially to theoutputs of counters 83-83'.

Still further employment of the invention is illustrated in FIG. 17wherein each encapsulated unit 85 in an array utilizes series-connectedcomponents which share adjacent encapsulations. Thus, for the case ofadjacent encapsulated units at locations x, y and z, the switchcomponent 30 at location x is in series with the averaging-resistorcomponent 32 at location y, the voltage-dividing resistor 31 beingconnected as already described. The arrangement will be seen tofacilitate preassembly of the series-connected elements 30-32, atprecise spacings, and relying upon mechanical flexibility of theirinterconnection at 186, the remaining lead of switch 30 being connectedto the upper lead end of resistor 31, and the remaining lead of resistor32 being connected to the bus 33.

Terminal connections to the FIG. 17 embodiment are made at A, B and C asdiscussed in connection with FIG. 5, except that at the remote end oflocation z the exposed lower-switch lead connection 187 must beconnected to the bus 33 via an additional averaging resistor 32', asshown.

Still further, FIG. 18 illustrates that the invention is not limited toinsertion of a flexible TLI-insert strip into a rigid tube, even forliquid-level measurement purposes. The TLI-insert strip in FIG. 18 willbe understood to be contained within a reinforced flexible hose 86 whichis terminated at its lower end by a suitable fitting 87 havingspring-connection 88 to a hook or eye 89 fixed to the bottom of the tank24. The upper end of hose 86 is shown clamped at 90 to jack means 91-92,by means of which spring tension at 88 may be initially set asnecessary. In use, it will be seen that flexibility of the switch arraycontained in hose 86 will permit the insert and its support to yield, asa liquid volume may be caused to displace laterally in the course of atanker vessel motion when at sea. In spite of such flexure, the abilityto respond to displacement of the float magnet remains unaffected.

What is claimed is:
 1. A tank-level measuring system, comprising anassembly of an elongate flexibly bendable tubular housing closed at itslower end, a magnet carrying float element encircling and guided by saidhousing for travel therealong as a function of the level of the fluidbeing measured, a flexibly bendable interconnected array of a pluralityof magnetically-sensitive electrical switch units in uniformly spacedand electrically interconnected successive longitudinal array within andalong the length of said tubular housing, said array being free forwithdrawal lengthwise from said housing and reinsertable at will, andelectrical-connection means connected to the upperunit end of saidarray; said assembly of housing and interconnected array beingnon-destructively bendable by virtue of its mechanical flexibilitywithout interfering with movement of said float.
 2. A tank-levelmeasuring system according to claim 1, in which said flexibly bendabletubular housing is a reinforced hydraulic-type hose.
 3. A tank-levelmeasuring system according to claim 1, in which the closed end of saidtubular housing includes tank-bottom anchoring means.
 4. In a tank-levelmeasuring system wherein an elongate vertical tubular housing is closedat its lower end and contains a removable longitudinally distributedarray of plural uniformly spaced electrically connected magneticallysensitive electrical switch units with electrical-connection means atthe upper end of said housing, and a permanently magnetized floatelement encircling and guided by said housing for travel therealongaccompanied by interaction with different switch elements as a functionof its buoyant position, the improvement wherein said tubular housing isnon-destructively bendable and in which said switch units areinterconnected by mechanically flexible means free of rigidification forenabling the array to bend with bending of said housing while retainingits removability and reinsertability as a unit lengthwise from and intosaid housing.
 5. The improvement of claim 4, wherein said tubularhousing is fixedly mounted to upper tank structure at its upper end andis resiliently connected at its lower end to the bottom of the tankstructure.
 6. In an apparatus for ascertaining the upper level of asupply of flowable material which is confined in a vessel and wherein aswitch-actuating element rides up and down along a vertically mountedhousing in the vessel and floats on said supply of flowable material atthe surface of said material to rise and fall with the level thereof,the combination, disposed as a removable and reinsertable unit withinsaid housing, of an elongated tubular sheath consisting of flexibleinsulating material; an elongated carrier consisting of a longitudinallysubstantially inelastic strip of flexible insulating material confinedin said sheath; and a plurality of electrical components mounted inlongitudinally spaced array on said carrier with electrical-connectionmeans at the upper end of said housing, said components including a rowof uniformly spaced-apart electric switches which extend in thelongitudinal direction of said carrier and each of which is actuatableby said element when the latter is in proximity to a respective switch,said carrier having said components so mounted thereon as to be readilyflexible without damage to said components so as to allow said carrierand said sheath, when outside of said housing, to be converted byflexing into a compact configuration occupying a volume whose maximumdimension is a small fraction of the length of said sheath.
 7. Thecombination of claim 6, wherein said carrier and sheath are sufficientlyflexible to permit forming convolutions each having a diameterapproximating that of the drum of an electrical cable spool.
 8. Thecombination of claim 6, wherein said components further comprise a rowof spaced-apart electrical resistors each of which is adjacent to one ofsaid switches.
 9. The combination of claim 8, wherein said resistors areconnected in series, and said components further comprise flexibleconductor means soldered to said resistors and to said switches.
 10. Ina tank-level measuring system wherein an elongate vertical tubularhousing is closed at its lower end and contains a removablelongitudinally distributed array of plural uniformly spaced electricallyconnected magnetically sensitive electrical switch units withelectrical-connection means at the upper end of said housing, and apermanently magnetized float element guided by said housing forinteraction with different switch elements as a function of its buoyantposition, the improvement wherein said tubular housing is curved over atleast a portion of its length and is effectively rigid, and in whichsaid switch units are interconnected by mechanically flexible means forenabling the array to bend and follow the curve of said housing duringfull insertion or removal of said array of switch units via the upperend of a tank-installed housing.